Integrated phase angle and optical critical dimension measurement metrology for feed forward and feedback process control

ABSTRACT

Methods and apparatus for controlling the critical dimensions and monitoring the phase shift angles of photomasks. Critical dimensions measurement data before wafer processing and after wafer processing are collected by an integrated metrology tool to adjust the process recipe, to determine if the critical dimensions are in specification and to determine if additional etching is required. Phase shift angle and uniformity across substrate measurement after wafer processing are collected by an integrated metrology tool to determine if the phase shift angle and its uniformity are in specification. The real time process recipe adjustment and determination if additional etching is requires allow tightening of the process control. The phase shift angle and uniformity monitoring allows in-line screening of phase shift photomasks.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/754,321, filed Jan. 9, 2004, which is incorporated by reference inits entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the fabrication of photomasks useful inthe manufacture of integrated circuits.

2. Background of the Related Art

Photolithography techniques use light patterns and photoresist materialsdeposited on a substrate surface to develop precise patterns on thesubstrate surface prior to the etching process. In conventionalphotolithographic processes, a photoresist is applied on the layer to beetched, and the features to be etched in the layer, such as contacts,vias, or interconnects, are defined by exposing the photoresist to apattern of light through a photolithographic photomask which correspondsto the desired configuration of features. A light source emittingultraviolet (UV) light, for example, may be used to expose thephotoresist to alter the composition of the photoresist. Generally, theexposed photoresist material is removed by a chemical process to exposethe underlying substrate material. The exposed underlying substratematerial is then etched to form the features in the substrate surfacewhile the retained photoresist material remains as a protective coatingfor the unexposed underlying substrate material. Since photomasks areused repeatedly to create device patterns, quality control of photomaskmanufacturing is very important.

Photolithographic photomasks, or reticles, include binary (orconventional) photomasks and phase shift masks (PSM), which could beused in sub 0.13 μm technology. Binary (or conventional) masks typicallyinclude a substrate made of an optically transparent silicon basedmaterial, such as quartz (i.e., silicon dioxide, SiO₂), having an opaquelight-shielding layer of metal, such as chromium, on the surface of thesubstrate. Phase shift masks improve the resolution of the aerial imageby phase shifting. The principle of phase shift mask is described in P.230-234 of Plummer, Deal and Griffin, “Silicon VLSI TechnologyFundamentals, Practice and Modeling”, 2000 by Prentice Hall, Inc. Phaseshift masks could be either attenuated phase shift or alternate phaseshift mask. An attenuated phase shift mask typically includes asubstrate made of an optically transparent silicon based material, suchas quartz, having a translucent layer of material, such as molybdenumsilicide (MoSi) or molybdenum silicon oxynitride (MoSiON), on top. Whenthe photolithographic light, e.g. at 248 nm wavelength, shines throughthe patterned mask surface covered by the translucent layer, thetransmission (e.g. 6% at 248 nm wavelength) and the thickness of thetranslucent layer create a phase shift, e.g., 180°, compared to thephotolithographic light that shines through the patterned mask surfacenot covered by the translucent layer. An alternate phase shift masktypically includes a substrate made of an optically transparent siliconbased material, such as quartz, which is etched to a certain depth tocreate a phase shift with the un-etched transparent substrate when thephotolithographic light shines through the patterned mask.

Photomasks allow light to pass therethrough in a precise pattern ontothe substrate surface. The metal layer on the photomask substrate ispatterned to correspond to the features to be transferred to thesubstrate. The patterns on the photomask could be 1×, 2× or 4× ofpatterns that will be patterned on the wafer substrate. Typically, aphotolithographic stepper reduces the image of the photomask by 4× andprints the pattern on the photoresist covering the wafer surface.Conventional photomasks are fabricated by first depositing one to twothin layers of metal, which could either be opaque or translucentdepending on the types of masks being formed, on a substrate comprisingan optically transparent silicon based material, such as quartz, anddepositing a photoresist layer on substrate. The photomask is thenpatterned using conventional laser or electron beam patterning equipmentto define the critical dimensions in the photoresist. The top metallayer, typically opaque, is then etched to remove the metal material notprotected by the patterned photoresist, thereby exposing the underlyingsilicon based material. For a binary mask, the photomask is formed afterthe metal etching step. While for attenuate and alternate phase shiftmasks, additional photoresist patterning and etching of transparentsubstrate or translucent metal layer are needed to form the photomask.

Since photomasks are used repeatedly to create device patterns, theaccuracy and tight distribution of the critical dimensions, and thephase shift angle and its uniformity across the substrate are keyrequirements for binary and phase shift photomasks. Critical dimensionsare defined here as the widths of features being measured and areaffected by etching process. Overetching could enlarge the dimension,while underetching could result in wider dimension distribution or metallayer not completely etched. In the case of phase shift masks, theaccuracy and tight distribution of the phase shift angle, typically180°, are also key requirements. For attenuated phase shift mask, thephase shift angle is affected by the thickness and transparency of thetranslucent metal layer (e.g. MoSi), while for alternate phase shiftmask, the phase angle is affected by the transparent material and itsetch depth.

A conventional method of controlling critical dimensions for thephotomasks comprises measuring the critical dimensions of the respectiveelements of the etched photomasks, statistically processing the resultsof such measurements, determining if the measurement passes therequirement, and adjusting the etch process performed on subsequentbatches of the substrate. Unfortunately, this method does not compensatefor substrate-to-substrate variations of the critical dimensions withina batch of substrates. Variables inherent to the etch process maybroaden distribution for the critical dimensions. This means that thepost-etch statistical distribution of the critical dimensions for etchedstructures may be broader than the pre-etch distribution of criticaldimensions of the etched structure of the photomask. As such, someetched structures may have critical dimensions outside a pre-determinedrange of acceptable values.

A conventional method of monitoring phase shift angle for the photomaskscomprises measuring the phase shift angles and the uniformity (ordistribution) of the photomasks, statistically processing the results ofsuch measurements, determining if the measurement passes therequirement, and adjusting the etch process performed on subsequentbatches of the substrate. Variables inherent to the metal filmdeposition processes that affect metal film thickness and metal filmtransparency of an attenuated phase shift mask could make the phaseshift angle measurement results of an attenuate phase shift photomaskoutside a pre-determined range of acceptable values. In addition,variables inherent to the etch process combined with the variables ofthe photomask lithography process may broaden the distribution of theetch depth, which affects phase shift angle and its uniformity for analternate phase shift mask. As such, some etched structures may havephase shift angles outside a pre-determined range of acceptable values.

Therefore, there remains a need in the art for an improved method andapparatus for controlling the critical dimensions and monitoring phaseshift angle and its uniformity of photomask in a semiconductor photomaskprocessing system.

SUMMARY OF THE INVENTION

The invention relates to a method and apparatus for controlling thecritical dimensions and monitoring phase shift angle and its uniformityof photomask during fabrication of semiconductor photomasks in asemiconductor photomask processing system.

Aspects of the invention generally provide methods and apparatus foretching a metal layer deposited on a silicon based substrate, such as aphotomask. In one aspect, a method of controlling the criticaldimensions of a photomask substrate comprises providing a photomasksubstrate with a metal layer on top, performing a photolithographicprocess on the photomask substrate, measuring the pre-etch criticaldimensions of the printed pattern by an integrated measuring tool,providing an initial etch recipe for a metal etch process, modifying theetch recipe based on the pre-etch critical dimension data, andperforming the etch process on the photomask substrate based on themodified etch recipe. In a further aspect, the method comprisesmeasuring post-etch critical dimensions of the etched pattern, andmodifying the initial etch recipe for the next photomask substrate basedon post-etch critical dimensions data. In yet another further aspect,the method comprises determining if the pre-etch critical dimensions arewithin specification, if the pre-etch critical dimensions are withinspecification, sending the substrate to the next process step, and ifthe pre-etch critical dimensions are out of specification, performingrework by removing photoresist from the substrate, and re-patterning thesubstrate with photoresist.

In another aspect, a method of monitoring the phase shift angle of aphase shift photomask comprises providing a photomask substrate with anetched metal layer, performing a photolithographic process on thephotomask substrate, etching the photomask substrate, removing theremaining photoresist, removing the remaining metal layer, and measuringthe phase shift angle and its uniformity across the substrate by anintegrated measuring tool. In a further aspect, the method comprisesdetermining if the measured data of phase shift angle and its uniformityacross the substrate are within specification, if the measured data arewithin specification, the photomask process sequence is complete, and ifthe measured data are out of specification, the photomask is marked outof specification.

In another aspect, a method of monitoring the phase shift angle of aphase shift photomask comprises providing a photomask substrate with alight-shielding metal layer on top of a translucent metal layer, whichis deposited on the substrate, performing a photolithographic process onthe photomask substrate, etching the light-shielding metal layer,removing the remaining photoresist, etching the translucent metal layer,removing the light-shielding metal layer, and measuring the phase shiftangle and its uniformity across the substrate by an integrated measuringtool. In a further aspect, the method comprises determining if themeasured data of phase shift angle and its uniformity across thesubstrate are within specification, if the measured data are withinspecification, considering the photomask process sequence is complete,and if the measured data are out of specification, marking the photomaskout of specification.

In another aspect, an apparatus for controlling the critical dimensionsof a photomask substrate comprises a photomask etch chamber forprocessing a photomask substrate, a measuring tool for measuringcritical dimension information prior to and after processing by theprocess chamber, and a computer system, coupled to the process chamberand the measurement tool, for storing the critical dimensioninformation.

In another aspect, an apparatus for monitoring the phase shift angles ofa phase shift photomask substrate comprises a process chamber forprocessing a substrate, a measuring tool positioned for measuring phaseshift angle and its uniformity across the substrate after the substrateis processed by the process chamber, and a computer system, coupled tothe process chamber and the measurement tool, for storing the measuredinformation.

In yet another aspect, an apparatus for controlling the criticaldimension and monitoring phase shift angles of a phase shift photomasksubstrate comprises a process chamber for processing a substrate, ameasuring tool positioned for measuring phase shift angle and itsuniformity across the substrate after the substrate is processed by theprocess chamber, a measuring tool positioned for measuring criticaldimension information prior to and after processing by the processchamber, and a computer system, coupled to the process chamber and themeasurement tool, for storing the critical dimension information.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited aspects of the inventionare attained and can be understood in detail, a more particulardescription of the invention, briefly summarized above, may be had byreference to the embodiments thereof which are illustrated in theappended drawings.

It is to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a flow chart illustrating one embodiment of a sequence forprocessing a substrate according to one embodiment of the invention.

FIG. 2 is a block diagram of key components of an integrated etchsystem.

FIGS. 3A-3F are cross-sectional views showing an etching sequence ofanother embodiment of the invention.

FIG. 4 is a flow chart illustrating one embodiment of a sequence forprocessing a substrate according to another embodiment of the invention.

FIGS. 5A-5G are cross-sectional views showing an etching sequence ofanother embodiment of the invention.

FIG. 6 is a schematic diagram of an etch chamber.

FIG. 7 is a diagram of one embodiment of an integrated etch system.

DETAILED DESCRIPTION

For convenience, the present invention is described herein primarilywith reference to the etching of phase shift masks. The invention can beused for etching of other types of photomasks. Phase shift photomasketching processes, for light-shielding layer, such as such as chromium,optically transparent material, such as quartz, and attenuatingmaterial, such as MoSi, could be dry etching processes. Plasmas ofetching gases, chlorine-containing gas (such as Cl₂) orfluorine-containing gas (such as SF₆ or CF₄), oxidizing gases, such asoxygen, and inert gases, such as helium, could be used to etch the metallayers formed on the substrate or the substrate itself. Details ofetching chemistries that are used to etch light-shielding layer for thisapplication have been disclosed in commonly assigned U.S. patentapplication Ser. No. 10/418,795, titled “Process For EtchingPhotomasks”, and filed on Apr. 18, 2003 and U.S. patent application Ser.No. 10/235,223, titled “Methods And Apparatus For Etching Metal Layerson Substrates”, and filed on Sep. 4, 2002. Etching of the silicon basedmaterial of the substrate is described in commonly assigned U.S. Pat.No. 6,534,417, titled “Method and Apparatus For Etching Photomasks”,issued Mar. 18, 2003 and U.S. Pat. No. 6,391,790, also titled “Methodand Apparatus For Etching Photomasks”, issued May 21, 2002. Details ofetching chemistries that are used to etch the translucent metal layerfor this application have been disclosed in commonly assigned U.S.patent application Ser. No. 10/437,729, titled “Methods for EtchingPhotolithographic Reticles”, filed on May 13, 2003. The disclosures ofall of these applications are incorporated herein by reference to theextent not inconsistent with aspects of the invention.

FIG. 1 is a flow chart of one embodiment of one process sequence of anetching process for an alternate phase shift photomask. The flow chartis provided for illustrative purposes and should not be construed aslimiting the scope of aspects of the invention. A photomask substrate,typically comprising a silicon based material, such as optical qualityquartz, is provided to a processing chamber at step 110. Suitable plasmaetch chamber includes the Tetra II™ photomask etch chamber 702 of FIG.7, or optionally, the Decoupled Plasma Source (DPS®) II processingchamber 600 of FIG. 6, both available from Applied Materials, Inc. ofSanta Clara, Calif. Other process chamber may be used to perform theprocesses of the invention. Photomask sizes range from three to nineinches squares, but most masks produced today are five or six inchessquare. The photomask substrate is then processed by depositing anopaque and conformal metal layer, for example chromium, on the substrateat step 120.

The dimensions of features to be formed in the metal layer are patternedby depositing and pattern etching a first resist material to expose theconformal metal layer at step 130. To ensure accurate and tightdistributions of pattern dimensions are printed on the photomask, thesubstrates with patterned photoresist layer are sent to an integratedcritical dimensions (CDs) measuring tool to determine pre-etch CDs andprofile at step 135. At step 136, the inspection results are used todetermine if the pre-etch CDs are within specification and the substrateshould be etched at step 140 or be reworked at step 137 and re-patternedwith photoresist at step 130. If the substrate should be etched, thepre-etch measurement results are used at step 140 to adjust processparameters (feedforward), such as etch time and/or etch parameters.

An example of a processing step that benefits from the completefeedforward solution of the present invention is etch processing that issensitive to incoming photoresist (PR) dimensions. The variation inincoming resist mask CD creates a proportional variation in the finaletched CD. Measuring the incoming resist CD prior to etching enables theetch process to be tuned to compensate for the variations due tolithography.

After etching, the wafer is optionally cleaned, as by an ash photoresiststrip followed by a wet cleaning step, and transferred back to theintegrated metrology unit, where the CDs, profile and depth of featuresformed by the etch process are measured by an integrated CD measuringtool and compared to the desired dimensions at step 140. Suchinformation can be fed back to the processor (e.g., to compensate foretch process drift) by adjustment of the etch recipe when etching thenext substrate.

By taking into account photoresist CD and profile variation whenchoosing an etch recipe, the present invention decouples post-etch CDfrom pre-etch CD and profile. By measuring the incoming resist CD andadjusting the process parameters, such as etch time, the etch processcan compensate for variations in lithography on successive wafers. Withautomatic compensation of incoming resist CD from the lithography step,a much tighter distribution of post-etch CD is achieved by the presentinvention, and the final CD uniformity becomes a realistic etchspecification without impacting the productivity of the etch tool.

To optimize production efficiency, post-etch measurements for closedloop control must be made directly on the wafer before it leaves theetcher. CDSEM (critical dimension scanning electron microscope)measurement can require time-consuming wet cleaning, particularly whenetch byproducts cling to the sidewalls of the etched structure. Suchdeposits render top-down CDSEM post-etch measurements inaccurate.Optical CD (OCD) metrology is insensitive to thin layers of deposits,making it possible to take accurate in-situ post-etch measurements,eliminate the cycle time penalty of wet cleaning, and immediately feedback data to the process controller.

After the post-etch CD measurement at step 145, the remaining resistmaterials are removed at step 146. The substrate may then be furtherprocessed to etch the silicon based material. The silicon based materialof the substrate is prepared for etching by depositing and patternetching a second resist material at step 150 to expose the substrate.The purpose of this substrate etch is to create an etch depth that willresult in uniform and desired phase shift angle, such as 180°.

The substrate is then transferred to a processing chamber, such as TetraII™ or DPS® II, where a processing gas mixture comprising afluorine-containing gas, such as CF₄, CHF₃ or C₂F₆, an oxidizing gas,such as oxygen, and an inert gas, such as helium, is introduced into theprocessing chamber and a plasma is generated, thereby etching theexposed silicon based material of the substrate at step 160. After thesubstrate is etched, the remaining photoresist is removed at step 161.At step 162, the remaining opaque metal layer is removed either by dryetch or wet etch.

After the remaining photoresist and opaque metal layer are removed, thesubstrate is sent to a phase shift angle measurement tool, to determinephase shift angle and its uniformity across the photomask substrate 165.Phase shift angles are collected on multiple locations across thesubstrate to measure its uniformity across the substrate.

At step 166, it is determined whether the phase shift angle anduniformity measurement fall within the specification. If so, at step 170the process sequence is considered complete. If the phase shift angleand uniformity measurement is out of the specification, the photomask ismarked as not meeting the requirement at step 171 and could bediscarded.

OCD (optical critical dimension) metrology techniques as employed by thepresent invention are advanced process control (APC) enablers andutilize novel technology to the CD measurement world where the currentSEM-based systems are becoming inadequate. For example, normal incidencespectroscopic OCD metrology systems provide detailed line profiles notpossible with in-line non-destructive SEMs. For photomasks, the OCDmetrology can operate under reflective mode (utilizing reflected light)or transmission mode (utilizing transmitted light). The compact size andspeed of OCD technology enables the measurement system of the presentinvention to be fully integrated into a process tool, such as AppliedMaterials' Tetra II™ or DPS® II etch system. When combined with APCsoftware, this provides a complete, feed-forward solution forwafer-to-wafer closed loop control. An example of the optical CDmeasuring tool is the Nano OCD 9000 available from Nanometrics ofMilpitas, Calif., or an optical imager as disclosed in U.S. Pat. No.5,963,329. The optical CD measuring tool can utilize scatterometry,reflectometry or transmission ellipsometry techniques.

Phase shift angle metrology techniques as employed by the presentinvention are also advanced process control (APC) enablers. It detectsthe reflected and transmitted light of a substrate over a broadwavelength range. The detected wavelength spectra are fitted to atheoretical model to enable the characterization of the film. Themetrology can be used to measure transparency, film thickness and phaseshift angle at multiple locations on the substrate. An example of thephase shift angel measuring tool is the n&k Analyzer 1512RT availablefrom n&k Technology, Inc. of Santa Clara, Calif.

An exemplary embodiment of the present invention is implemented using acritical dimension or phase shift angle measuring tool in a processingline 200, as shown in FIG. 2, comprising a measuring tool 210, e.g., anoptical CD measuring tool or a phase shift angle measuring tool.Processing line 200 further comprises a processor 220, which performsthe analysis disclosed herein electronically, and a monitor 230 fordisplaying results of the analyses of processor 220. Processor 220 canbe in communication with a memory device 240, such as a semiconductormemory, and a computer software-implemented database system 250 known asa “manufacturing execution system” (MES) conventionally used for storageof process information. Processor 220 can also be in communication withprevious process tool 260 and etcher 270.

FIGS. 3A-3F illustrate the composition of the photomask prior to theetching steps as well as further illustrate the process described abovein FIG. 1. A substrate 300 is introduced into a processing chamber. Thesubstrate 300 (or reticle) comprises a base material of an opticallytransparent material 310, for example, optical quality quartz, calciumfluoride, alumina, sapphire, or combinations thereof, typically made ofoptical quality quartz material. An opaque (or light-shielding) metallayer 320, such as chromium, is deposited on the optically transparentmaterial 310 as shown in FIG. 3A. The light-shielding metal layer, suchas chromium layer, may be deposited by conventional methods known in theart, such as by physical vapor deposition (PVD) or chemical vapordeposition (CVD) techniques. The light-shielding (or opaque) metal layer320 is typically deposited to a thickness between about 50 and about 150nanometers (nm) thick, however, the depth of the layer may change basedupon the requirements of the manufacturer and the composition of thematerials of the substrate or metal layer.

Referring to FIG. 3B, the substrate 300 is then transferred to anotherprocessing chamber where a layer of resist material 330, such as“RISTON,” manufactured by Du Pont de Nemours Chemical Company, isdeposited upon the opaque metal layer 320 to a thickness between about200 and 600 nm thick. The resist material 330 is then pattern etchedusing conventional laser or electron beam patterning equipment to form afirst opening 325 which is used to define the dimensions of the secondopening 335 to be formed in the opaque metal layer 320.

The substrate 300 is then transferred to an etch chamber, such as theTetra II™ photomask etch chamber described in FIG. 7 or DPS® IIprocessing chamber 600 described in FIG. 6 (see below), and thelight-shielding metal layer 320 is etched using metal etching techniquesknown in the art or by new metal etching techniques that may bedeveloped to form the second opening 335 which expose the underlyingtransparent material 310 as shown in FIG. 3C. Details of etchingchemistries that are used to etch the light-shielding metal layer forthis application have been disclosed in commonly assigned U.S. patentapplication Ser. No. 10/418,795, titled “Process For EtchingPhotomasks”, and filed on Apr. 18, 2003 and U.S. patent application Ser.No. 10/235,223, titled “Methods And Apparatus For Etching Metal Layerson Substrates”, and filed on Sep. 4, 2002.

Referring to FIGS. 3A-3C, after etching of the light-shielding metallayer 320 is completed, the substrate 300 is transferred to a processingchamber, and the remaining resist material 330 is usually removed fromthe substrate 300, such as by an oxygen plasma process, or other resistremoval technique known in the art.

Referring to FIGS. 3D-3F, the substrate 300 may be further processed byetching the transparent material 310. In etching the transparentmaterial 310, the resist material 330 is removed and a second resistmaterial 340 is applied and patterned to expose the underlyingtransparent material 310 within the second opening 335. The resistmaterial is deposited to a depth between about 200 nm and 600 nm thick,but may be of any thickness and may also be of the same thickness as thedepth of the features to be etched in the transparent material 310 toform the photomask. The substrate 300 is then etched to form a thirdopening 345 in the resist layer 340, the metal layer 320, and thetransparent material 310. The patterned substrate 300 is thentransferred to an etch chamber, such as the Tetra II™ photomask etchchamber 702 of FIG. 7 or DPS® II processing chamber 600 of FIG. 6 (seebelow), for plasma etching the transparent material 310. The secondresist material 340 is then removed to form a patterned substratesurface 355. Afterwards, the metal layer 320 is removed to form apatterned substrate surface 365.

For attenuated phase shift mask, the phase shift angle is affected bythe translucent metal, such as MoSi, film thickness and its filmtransparency. FIG. 4 is a flow chart of one embodiment of one processsequence of an etching process. The flow chart is provided forillustrative purposes and should not be construed as limiting the scopeof aspects of the invention. A substrate is provided to a processingchamber at step 410, such as the Tetra II™ photomask etch chamber 702 ofFIG. 7 or DPS® II processing chamber 600 of FIG. 6 (see below). Thesubstrate 300 (or reticle) comprises a base material of an opticallytransparent material 310, for example, optical quality quartz, calciumfluoride, alumina, sapphire, or combinations thereof, typically made ofoptical quality quartz material. The substrate is then processed bydepositing a translucent and conformal metal layer, for examplemolybdenum silicide (MoSi), on the substrate at step 415, followed bydepositing an opaque (or light-shielding) and conformal metal layer atstep 420, such as chromium. Afterwards, the substrate is deposited andpatterned with photoresist 430. To ensure accurate and tightdistribution of pattern dimensions are printed on the photomask, at step435 the substrates with patterned photoresist layer are sent to acritical dimension measurement tool to determine pre-etch CD andprofile, then at step 436 the measurement results are used to determineif the pre-etch CDs are within specification, and the substrate shouldbe etched at step 440 or be reworked at step 437 and re-patterned withphotoresist at step 430. If the substrate should be etched, at step 440the pre-etch measurement results are used to adjust process parameters,such as etch time and/or etch parameters.

After the substrate is etched and measured with critical dimensions, atstep 447 the photoresist is stripped from the substrate surface. Thesubstrate is then sent to an etch chamber at step 450 to etch thetranslucent metal layer (e.g. MoSi) using the patterned opaque metal(e.g. Cr) layer as a mask.

After the etching of the translucent metal layer, at step 460 the opaquemetal layer is removed from the substrate surface. The substrate is thensent, at step 465, to a phase shift angle measurement tool to determinethe film transparency, phase shift angle and phase shift angleuniformity across the photomask substrate. Phase shift angle forattenuated phase shift mask is determined by the thickness andtransparency of the translucent film. The phase shift angles arecollected on multiple locations across the substrate to measure itsuniformity across the substrate. At step 466, it is determined whetherthe transparency, phase shift angle and phase shift angle uniformitymeasurement fall within the specification 466. If so, the substrateprocess sequence is complete at step 470. If the transparency, phaseshift angle and phase shift angle uniformity measurement is out of thespecification, the photomask is marked out of specification at step 471and could be discarded.

FIGS. 5A-5G illustrate the composition of the photomask prior to theetching steps as well as further illustrate the process described abovein FIG. 4. A substrate 500, typically made of optical quality quartzmaterial 510, is introduced into a processing chamber. A translucentmetal layer 520, such as MoSi, is deposited on the transparent material510 as shown in FIG. 5A. The translucent metal layer may be deposited byconventional methods known in the art, such as by physical vapordeposition (PVD) or chemical vapor deposition (CVD) techniques. Thetranslucent metal layer 520 is typically deposited to a thicknessbetween about 50 and about 150 nanometers (nm) thick, however, the depthof the layer may change based upon the requirements of the manufacturerand the composition of the materials of the substrate or metal layer.

Referring to FIG. 5B, the substrate 500 is deposited with an opaquemetal layer 530, such as chromium, on the translucent metal layer 520.The opaque (or light-shielding) metal layer may be deposited byconventional methods known in the art, such as by physical vapordeposition (PVD) or chemical vapor deposition (CVD) techniques. Theopaque layer 530 is typically deposited to a thickness between about 50and about 150 nanometers (nm) thick, however, the depth of the layer maychange based upon the requirements of the manufacturer and thecomposition of the materials of the substrate or metal layer.

Referring to FIG. 5C, the substrate 500 is then transferred to anotherprocessing chamber where a layer of resist material 540, such as“RISTON,” manufactured by Du Pont de Nemours Chemical Company, isdeposited upon the opaque metal layer 530 to a thickness between about200 and 600 nm thick. The resist material 540 is then pattern etchedusing conventional laser or electron beam patterning equipment to form afirst opening 525 which is used to define the dimensions of the secondopening 535 to be formed in the opaque metal layer 530.

The substrate 500 is then transferred to an etch chamber, such as aTetra II™ or a DPS® II processing chamber, and the opaque layer 530 isetched using metal etching techniques known in the art or by new metaletching techniques described above that may be developed to form thesecond opening 535 which exposes the underlying translucent metal layer520 as shown in FIG. 5D.

Referring to FIGS. 5A-5D, after etching of the opaque metal layer 530 iscompleted, the substrate 500 is transferred to a processing chamber, andthe remaining resist material 540 is usually removed from the substrate500, such as by an oxygen plasma process, or other resist removaltechnique known in the art.

Referring to FIGS. 5E, 5F and 5G, the substrate 500 may be furtherprocessed by etching the translucent metal layer 520. In etching thetranslucent metal layer 520, the etched opaque metal layer is used tocreate an etching pattern. The substrate 500 is then etched to form anopening 555 in the opaque metal layer 530, the translucent metal layer520, and the transparent material 510. The remaining opaque metal layer530 is removed to form a patterned substrate surface 565.

Aspects of the invention will be described below in reference to aninductively coupled plasma etch chamber that includes the Tetra II™photomask etch chamber or the Decoupled Plasma Source, or DPS® II,chamber, both manufactured by Applied Materials, Inc., of Santa Clara,Calif. Other process chambers may be used to perform the processes ofthe invention, including, for example, capacitively coupled parallelplate chambers and magnetically enhanced ion etch chambers as well asinductively coupled plasma etch chambers of different designs. Althoughthe processes are advantageously performed with the Tetra II™ photomasketch chamber, the description in conjunction with the DPS® II processingchamber is illustrative, and should not be construed or interpreted tolimit the scope of aspects of the invention.

FIG. 6 depicts a schematic diagram of an exemplary Decoupled PlasmaSource (DPS®) II etch reactor 600 that may illustratively be used topractice the invention. The DPS® II reactor 600 is a processing moduleof a Centura® integrated semiconductor wafer processing system availablefrom Applied Materials, Inc. of Santa Clara, Calif. The particularembodiment of the reactor 600 shown herein is provided for illustrativepurposes and should not be used to limit the scope of the invention.

The reactor 600 generally comprises a process chamber 610 having asubstrate pedestal 616 within a conductive body (wall) 630, and acontroller 640. The chamber 610 is supplied with a substantially flatdielectric ceiling 620. Other modifications of the chamber 610 may haveother types of ceilings, e.g., a dome-shaped ceiling. Above the ceiling620 is disposed an antenna 612 comprising one or more inductive coilelements (two co-axial elements 612 a and 612 b are shown) that may beselectively controlled. The antenna 612 is coupled, through a firstmatching network 619, to a plasma power source 618. The plasma powersource 618 typically is capable of producing up to 3000 W at a tunablefrequency in a range from 50 kHz to 13.56 MHz.

The substrate pedestal (cathode) 616 is coupled, through a secondmatching network 624, to a biasing power source 622. The biasing source622 generally is a source of up to 500 W at a frequency of approximately13.56 MHz that is capable of producing either continuous or pulsedpower. In other embodiments, the source 622 may be a DC or pulsed DCsource.

A controller 640 comprises a central processing unit (CPU) 644, a memory642, and support circuits 646 for the CPU 644 and facilitates control ofthe components of the process chamber 610 and, as such, of the etchprocess, as discussed below in further detail.

An etchant gas and a passivation gas are provided to the process chamber610 from a gas panel 638. The etchant gas is typically supplied throughone or more inlets 626 (two inlets are shown) located above thesubstrate pedestal 616. The passivation gas is supplied from the gaspanel 638 through a plurality of inlets 628 (e.g., openings, injectors,and the like). The inlets 628 (two inlets are shown) are generallylocated substantially equidistantly around the substrate pedestal 616approximately coplanar with a semiconductor wafer 614 being etched.Embodiment and location of the inlets 628 are selected to provide highcontrolled concentration of the passivation gas in a peripheral region(i.e., annular region near the edge) of the wafer 614.

The etchant gas and the passivation gas are delivered to the processchamber 610 using separate gas conduits (conduits 637 and 639,respectively) and do not mix until they are dispersed into a reactionvolume 653 of the chamber. In the depicted embodiment, the etchant gasis provided to the inlets 626 using an annular gas channel 627 and,similarly, the passivation gas is provided to the inlets 628 using anannular gas channel 629. The gas channels 627 and 629 may be formed inthe wall 630 or in gas rings (as shown) that are coupled to the wall630. In the process chamber 610, the etchant and passivation gases forma gaseous mixture 650. During an etch process, the gaseous mixture 650is ignited into a plasma 655 by applying power from the plasma source618 to the antenna 612.

The gas pressure in the chamber 610 is controlled using a throttle valve677 and a vacuum pump 662. The temperature of the wall 630 may becontrolled using liquid-containing conduits (not shown) that run throughthe wall 630. Typically, the chamber wall 630 is formed from a metal(e.g., aluminum (Al), stainless steel, and the like) and coupled to anelectrical ground 634.

In operation, the temperature of the wafer 614 is controlled bystabilizing a temperature of the substrate pedestal 616. In oneembodiment, a backside gas (e.g., helium (He)) from a gas source 648 isprovided via a gas conduit 649 to channels that are formed in thepedestal surface under the wafer 614. The backside gas is used tofacilitate heat transfer between the pedestal 616 and the wafer 614.During the processing, the pedestal 616 may be heated by an embeddedresistive heater 632 to a steady-state temperature and then the heliumgas facilitates uniform heating of the wafer 614. Using such thermalcontrol, the wafer 614 may be maintained at a temperature between about0 and 350 degrees Celsius.

In one embodiment, the substrate pedestal 616 comprises an electrostaticchuck 660, an edge ring 615, the resistive heater 632, a heat sink 666,and a mounting assembly 606. The electrostatic chuck 660 comprises atleast one clamping electrode 680 and is controlled by a chuck powersupply 676. The resistive heater 632 generally comprises at least oneheating element 682 and is regulated by a heater power supply 678. Inalternative embodiments, the substrate pedestal 616 may comprise asusceptor clamp ring, a mechanical chuck, and the like substrateretention mechanism.

In operation, the lift mechanism 692 is used to raise the substrate 614off the substrate support 616 or to lower the substrate onto thesubstrate support. Generally, the lift mechanism 162 comprises aplurality of lift pins 672 (one lift pin is shown) that travel throughrespective guide holes 688. The process chamber 610 also comprisesconventional systems for process control, internal diagnostic, end pointdetection, and the like. Such systems are collectively shown as supportsystems 607.

Those skilled in the art will understand that other forms of etchchambers may be used to practice the invention, including chambers withremote plasma sources, electron cyclotron resonance (ECR) plasmachambers, and the like.

To facilitate control of the process chamber 610, the controller 640 maybe one of any form of general-purpose computer processor that can beused in an industrial setting for controlling various chambers andsub-processors. The memory, or computer-readable medium, 642 of the CPU644 may be one or more of readily available memory such as random accessmemory (RAM), read only memory (ROM), floppy disk, hard disk, or anyother form of digital storage, local or remote. The support circuits 646are coupled to the CPU 644 for supporting the processor in aconventional manner. These circuits include cache, power supplies, clockcircuits, input/output circuitry and subsystems, and the like. Theinventive method is generally stored in the memory 642 as a softwareroutine. Alternatively, such software routine may also be stored and/orexecuted by a second CPU (not shown) that is remotely located from thehardware being controlled by the CPU 644.

An example of an etch system that is integrated with an ex-situmetrology tool with the capability of measuring CDs and phase shiftangle is shown in FIG. 7. The system, Tetra II™, comprises a chamber or“mainframe” 701, such as the Centura™ processing system available fromApplied Materials, Inc. of Santa Clara, Calif., for mounting a pluralityof processing chambers, e.g., Tetra II™ photomask reactors (or chambers)702, and one or more transfer chambers 703, also called “load locks”. Inone embodiment of the present invention, four etch reactors 702 aremounted to the mainframe 701. In one exemplary embodiment, three etchers702 are used for etching and one is optionally used for post-etchcleaning (i.e. removing photoresist polymers and other residue fromwafers after etching). A robot 704 is provided within the mainframe 701for transferring wafers between the processing reactors 702 and thetransfer chambers 703. The transfer chambers 703 are connected to afactory interface 705, also known as a “mini environment”, whichmaintains a controlled environment. Metrology (or measurement) tools706, such as CD measuring tool or phase angle measurement tool, areintegrated in the load lock area 705 and with high-speed data collectionand analysis capabilities. Sampled wafer or every wafer that enters thesystem 700 is measured for thickness before and after etch processing.The metrology tool 706 could also be placed at different location withinthe process system 700. Cassette holders 708 are connected to the otherend of the factory interface 705. 709 could be configured to be acassette holder (same as 708) or to place a metrology tool (same as706). A robot 707 is placed inside 705 to transfer substrate betweencassette holders (708 and possibly 709), measuring tools (706 andpossibly 709) and “load locks” (703). One or more of the processchambers 702 could also be deposition chambers, since the concept of theinvention also applies to deposition process.

While the foregoing is directed to the preferred aspects of theinvention, other and further aspects of the invention may be devisedwithout departing from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. An apparatus for controlling the critical dimensions of a photomasksubstrate, comprising: a photomask etch chamber for processing aphotomask substrate; a measuring tool for measuring critical dimensioninformation prior to and after processing by the process chamber; and acomputer system, coupled to the process chamber and the measurementtool, for storing the critical dimension information.
 2. The apparatusof claim 1, wherein the measuring tool can operate under eitherreflective mode or transmission mode.
 3. The apparatus of claim 1further comprising: a controller coupled to the etch chamber and incommunication with the computer system; and computer readable mediacontaining instructions, that when executed by the controller, cause theetch chamber to perform a method for controlling critical dimensions ofa photomask substrate comprising: measuring pre-etch critical dimensionsof a printed photolithographic pattern formed a metal layer disposed ona photomask substrate the measuring tool; providing an initial etchrecipe for a metal etch process to be preformed in the etch chamber;modifying the etch recipe based on the pre-etch critical dimension dataof said photomask substrate; performing the etch process on saidphotomask substrate in the etch chamber based on the modified etchrecipe to form an etched pattern on said photomask substrate; andmeasuring post-etch critical dimensions of the etched pattern.
 4. Theapparatus of claim 3, wherein the computer readable media containsinstructions, that when executed by the controller, cause the method tofurther comprise; modifying the initial etch recipe for the nextphotomask substrate based on the post-etch critical dimensions data. 5.The apparatus of claim 1 further comprising: a controller coupled to theetch chamber and in communication with the computer system; and computerreadable media containing instructions, that when executed by thecontroller, cause the etch chamber to perform a method for controllingcritical dimensions of a photomask substrate comprising: etching thefeatures according to an etch recipe to be performed in the etch chamberfor specified critical dimensions of the features modified based on ameasured pre-etch critical dimensions of the features by the measuringtool; measuring the features to determine conformity with the specifiedcritical dimensions by the measuring tool; determining from themeasurement the modifications of the etch recipe required to conform tothe specified critical dimensions; and etching another photomasksubstrate in the etch chamber according to the modified etch recipe. 6.An apparatus for monitoring the phase shift angles of a phase shiftphotomask substrate, comprising: a process chamber for processing asubstrate; a measuring tool positioned for measuring phase shift angleand its uniformity across the substrate after the substrate is processedby the process chamber; and a computer system, coupled to the processchamber and the measurement tool, for storing the measured information.7. The apparatus of claim 6 wherein the process chamber is an etchchamber.
 8. The apparatus of claim 6 further comprising: a controllercoupled to the etch chamber and in communication with the computersystem; and computer readable media containing instructions, that whenexecuted by the controller, cause the etch chamber to perform a methodfor controlling critical dimensions of a photomask substrate comprising:measuring pre-etch critical dimensions of a printed photolithographicpattern formed a metal layer disposed on a photomask substrate themeasuring tool; providing an initial etch recipe for a metal etchprocess to be preformed in the etch chamber; modifying the etch recipebased on the pre-etch critical dimension data of said photomasksubstrate; performing the etch process on said photomask substrate inthe etch chamber based on the modified etch recipe to form an etchedpattern on said photomask substrate; and measuring post-etch criticaldimensions of the etched pattern.
 9. The apparatus of claim 8, whereinthe computer readable media contains instructions, that when executed bythe controller, cause the method to further comprise; modifying theinitial etch recipe for the next photomask substrate based on thepost-etch critical dimensions data.
 10. The apparatus of claim 6 furthercomprising: a controller coupled to the etch chamber and incommunication with the computer system; and computer readable mediacontaining instructions, that when executed by the controller, cause theetch chamber to perform a method for controlling critical dimensions ofa photomask substrate comprising: etching the features according to anetch recipe to be performed in the etch chamber for specified criticaldimensions of the features modified based on a measured pre-etchcritical dimensions of the features by the measuring tool; measuring thefeatures to determine conformity with the specified critical dimensionsby the measuring tool; determining from the measurement themodifications of the etch recipe required to conform to the specifiedcritical dimensions; and etching another photomask substrate in the etchchamber according to the modified etch recipe.
 11. An apparatus forcontrolling the critical dimension and monitoring phase shift angles ofa phase shift photomask substrate, comprising: a process chamber forprocessing a substrate; a measuring tool positioned for measuring phaseshift angle and its uniformity across the substrate after the substrateis processed by the process chamber; a measuring tool positioned formeasuring critical dimension information prior to and after processingby the process chamber; and a computer system, coupled to the processchamber and the measurement tool, for storing the critical dimensioninformation.
 12. The apparatus of claim 11 wherein the process chamberis an etch chamber.
 13. The apparatus of claim 11 further comprising: acontroller coupled to the etch chamber and in communication with thecomputer system; and computer readable media containing instructions,that when executed by the controller, cause the etch chamber to performa method for controlling critical dimensions of a photomask substratecomprising: measuring pre-etch critical dimensions of a printedphotolithographic pattern formed a metal layer disposed on a photomasksubstrate the measuring tool; providing an initial etch recipe for ametal etch process to be preformed in the etch chamber; modifying theetch recipe based on the pre-etch critical dimension data of saidphotomask substrate; performing the etch process on said photomasksubstrate in the etch chamber based on the modified etch recipe to forman etched pattern on said photomask substrate; and measuring post-etchcritical dimensions of the etched pattern.
 14. The apparatus of claim13, wherein the computer readable media contains instructions, that whenexecuted by the controller, cause the method to further comprise;modifying the initial etch recipe for the next photomask substrate basedon the post-etch critical dimensions data.
 15. The apparatus of claim 11further comprising: a controller coupled to the etch chamber and incommunication with the computer system; and computer readable mediacontaining instructions, that when executed by the controller, cause theetch chamber to perform a method for controlling critical dimensions ofa photomask substrate comprising: etching the features according to anetch recipe to be performed in the etch chamber for specified criticaldimensions of the features modified based on a measured pre-etchcritical dimensions of the features by the measuring tool; measuring thefeatures to determine conformity with the specified critical dimensionsby the measuring tool; determining from the measurement themodifications of the etch recipe required to conform to the specifiedcritical dimensions; and etching another photomask substrate in the etchchamber according to the modified etch recipe.